Anyone who lives near the Underground (Subway) in London will also be exposed to large fields as the trains run on dc and tend to pulseate as the contact with the rail/cantenary varies.
You could only effectively sheild with some kind of ferrous material which would be impractable for a whole house.
In any case, at what level is the increased risk? We have Radon gas seeping into some houses here, and people still smoke cigarettes!
